Multilayer container of polyglycolic acid and polyester and blow molding production process

ABSTRACT

The invention provides a multilayer container that comprises a polyglycolic acid layer and a thermoplastic polyester resin layer and is much improved in terms of gas barrier properties, heat resistance, moldability, transparency and durability, and its production process. Polyglycolic acid is used as a gas barrier resin. At the body and bottom, the thermoplastic polyester resin forms an inner and an outer layer, and an intermediate layer comprising at least one polyglycolic acid layer is embedded in the thermoplastic polyester resin layer. The opening end of the container is formed of a thermoplastic polyester resin layer alone, and the body is biaxially oriented. The multilayer container has heat resistance enough to stand up to hot-filling at 93° C. for 20 seconds.

TECHNICAL FIELD

The present invention relates generally to a multilayer container thatat least comprises a polyglycolic acid layer and a thermoplasticpolyester resin layer, and more specifically to a multilayer containerthat has a structure wherein an intermediate layer comprising at leastone. polyglycolic acid layer is embedded in a thermoplastic polyesterresin layer, and is improved in terms of gas barrier properties, heatresistance, moldability, transparency and durability. The presentinvention is also concerned with a process for producing said multilayercontainer by co-injection stretch blow molding. The multilayer containeraccording to the invention, taking advantage of its properties, findsapplications as containers for drinks and foods such as carbonated fruitjuices, lactic drinks, beers, wines, soy sauces, sauces, jams, jellies,soups, and salad oils.

BACKGROUND ART

In recent years, blow molded containers of thermoplastic resins havebeen developed in the form of containers for a variety of drinks andfoods. Now, single-layer PET bottles comprising polyethyleneterephthalate (PET) are commonly used as such blow molded containers.

However, the PET bottles are found to be less than satisfactory forcontainers for stuffs sensitive to oxygen, and so are required to havegas barrier properties in general, and carbonic acid gas barrierproperties for carbonated beverages as well. When liquid food stuffssuch as jams, jellies and fruit sauces are packed in blow moldedcontainers, this is generally achieved by hot-filling. Also carbonatedfruit juices or lactic drinks, etc. are heat sterilized by hot-watershowering upon packed in blow molded containers. Thus, the blow moldedcontainers are required to have properties high enough to stand up toheat and pressure. To sum up, the blow molded containers must possesshigh gas barrier properties and heat resistance enough to be resistantto hot-filling.

To improve the gas barrier properties of blow molded containers, someprocesses have already been proposed, wherein a multilayer containerwith a gas barrier resin layer provided in an intermediate layer isformed by blow molding.

JP-A 56-64839 proposes a multilayer container production process whereina container precursor having a multilayer structure comprising an outerPET layer and an inner PET layer with an intermediate layer formed of amethaxylene group-containing polyamide resin, and then subjected tobiaxial stretch blow molding.

JP-A 57-128516 comes up with a blow molded container having a multilayerstructure comprising at least two thermoplastic resins, wherein at leasta thin portion of its body has a three- or multi-layer structure, atleast the end of its opening has a single structure, and at least thethin portion of its body has a biaxially oriented multilayer structure.This publication describes that PET is used as the thermoplastic resinthat forms the inner and outer layers and the end of the opening, andEVOH or a methaxylene group-containing polyamide resin is used for theintermediate layer.

JP-A 62-199425 discloses a process for producing a biaxially stretchedcontainer, wherein a multilayer pre-molding article comprising an innerPET layer and an outer PET layer with at least one intermediate layercomprising a gas barrier resin is subjected to biaxially stretch blowmolding in a mold held at a thermally fixed temperature and the blowmolded article is heat treated, after which the blow molded article iscooled and removed from the mold. An example where EVOH and a xylenegroup-containing polyamide resin are used is set forth in thatpublication.

Since the 1990s, multilayer containers having a structure of, forinstance, PET/EVOH/PET or PET/MXD6/PET layer construction and obtainedby co-injection stretch blow molding, for instance, in container formsfor beers or wines, have already been commercially put on the market.

Since EVOH has a melting point close to a thermal decompositiontemperature, a high melt viscosity, etc., however, it is considerablydifficult to subject EVOH in combination with PET to co-injectionstretch blow molding. More exactly, it is difficult to determineconditions for co-injection stretch blow molding of two such resins,because there is a large difference in proper molding temperaturebetween them. Upon high temperature injection, for instance, the meltingtemperature becomes high by crosslinking (gelation) of EVOH, ending upwith instable melt flows. This inevitably causes the intermediate layeror the EVOH layer to vary largely in thickness, and implanting height(height from the bottom of a bottle to the tip of the EVOH layer) tobecome unsatisfactory or vary, resulting in lack of gas barrierproperties and defective appearance.

On the other hand, MXD6 nylon that is a typical methaxylenegroup-containing polyamide resin possesses very excellent co-injectioncapability when used in combination with PET, because of having amelting point close to that of PET. In addition, since both resins havean approximate glass transition temperature, it is easy to determine aproper molding temperature for stretch blow molding. However, MXD6 nylonis less satisfactory than EVOH in terms of gas barrier properties, andso a blow molded container with an MXD6 nylon intermediate layer doesnot lend itself to applications where oxygen barrier properties areneeded over an extended period of time or high gas barrier propertiesare demanded.

JP-A 61-47337 discloses a process for producing a multilayer bottle oflayer construction comprising PET/HBR/PET by co-injection stretch blowmolding, wherein a resin obtained by polycondensation of dimethylterephthalate and ethylene glycol is mixed with a resin obtained byring-opening of glycolide at various mixing ratios, the mixture is meltpolymerized to obtain a polymer (HBR) having high gas barrierproperties, and the HBR and PET are subjected to co-injection stretchblow molding. However, the oxygen gas barrier properties of the HBR setforth in that publication is not sufficiently elevated, say, on theorder of 2.3×10⁻¹³ cm³·cm/cm²·sec·cmHg at best, as estimated by anoxygen permeability coefficient (PO₂) measured at 25° C. Thatpublication says nothing specific to a heat-resistant blow moldedcontainer having heat resistance enough to stand up to hot-filling.

JP-A 10-138371 discloses a gas barrier, multilayer hollow containerhaving a multilayer wall construction wherein a thermoplastic resinlayer is laminated on at least one side of a layer formed ofpolyglycolic acid. That publication sets forth a process for producing amultilayer hollow container by multilayer extrusion blow molding,multilayer injection blow molding or the like, and gives a specificexample of producing a multilayer hollow container comprising an innerPET layer and an outer PET layer with a polyglycolic acid intermediatelayer interleaved between them via an adhesive layer by means ofco-injection stretch blow molding. With such multilayer hollowcontainers produced by co-injection stretch blow molding as described inthat publication, however, there is still much to be desired in terms ofco-injection stretch blow molding conditions, gas barrier properties,durability, heat resistance, moldability, etc. More specifically, theproblems to be challenged are to enhance durability by reliableembedding of a polyglycolic acid layer that is susceptible to decomposeunder environmental conditions in a thermoplastic resin layer, improvegas barrier properties, and achieve heat resistance enough to stand upto hot-filling.

DISCLOSURE OF THE INVENTION

A primary object of the invention is to provide a multilayer containerthat is much more improved in terms of gas barrier properties, heatresistance, moldability, transparency and durability, and its productionprocess.

The inventors have carried out an extensive investigation with a viewtowered achieving the above object. As a result it has been found that amultilayer container that at least comprises a polyglycolic acid layerand a thermoplastic polyester resin layer, and has a high level of gasbarrier properties and heat resistance enough to stand up to hot-fillingand excellent in transparency as well can be obtained by using apolyglycolic acid excellent in gas barrier properties as an intermediatelayer, and embedding the polyglycolic acid entirely in the thermoplasticpolyester resin layer so that the polyglycolic acid layer is protectedfrom hydrolysis, etc., while the type of thermoplastic polyester resinand molding conditions for co-injection stretch blow molding areselected.

The inventors have also found that relations among melt viscosities ofthe respective resins upon co-injection molding as well as suitableranges for temperature conditions, stretch factors, etc. upon stretchblow molding can be properly determined by a combined use ofpolyglycolic acid and thermoplastic polyester resin. Further, theinventors have found that if the biaxial orientation of a container bodyis thermally fixed during stretch blow molding where, for instance, PETis used as the thermoplastic polyester resin, then heat resistance canbe much more improved. Such findings have underlain the presentinvention.

Thus, the present invention provides a multilayer container that atleast comprises a polyglycolic acid layer and a thermoplastic polyesterresin layer, wherein:

(a) said polyglycolic acid is a gas barrier resin that contains arepeating unit represented by formula (1) at a proportion of at least60% by weight and has an oxygen permeability coefficient of up to5.0×10⁻¹⁴ (cm³·cm/cm²·sec·cmhg) as measured at a temperature of 23° C.and a relative humidity of 80% pursuant to JIS K-7126, Formula (1)

(b) at a body and a bottom of the multilayer container, thethermoplastic polyester resin forms an inner layer and an outer layer,

(c) at the body and the bottom of the multilayer container, anintermediate layer comprising at least one polyglycolic acid layer isembedded in the thermoplastic polyester resin layer,

(d) an end of an opening in the multilayer container is formed of athermoplastic polyester resin layer alone,

(e) the body of the multilayer container is biaxially oriented, and

(f) the multilayer container is of heat resistance enough to stand up tohot-filling at 93° C. for 30 seconds.

The present invention also provides a multilayer container productionprocess involving the steps of co-injecting at least polyglycolic acidand a thermoplastic polyester resin to form a bottomed multilayerpreform, and then subjecting said multilayer preform to biaxial stretchblow molding, thereby producing a multilayer container, characterized inthat:

(I) said polyglycolic acid is a gas barrier resin that contains arepeating unit represented by formula (1) at a proportion of at least60% by weight and has an oxygen permeability coefficient of up to5.0×10⁻¹⁴ (cm³·cm/cm²·sec·cmHg) as measured at a temperature of 23° C.and a relative humidity of 80% pursuant to JIS K-7126, Formula (1)

(II) a molding machine equipped with a plurality of injection cylindersis used to co-inject resin melts through one gate into-a single preformmold cavity by successive or concurrent molding in one clampingoperation, thereby making a bottomed, multilayer preform comprising (A)an inner layer and an outer layer, each composed of a thermoplasticpolyester resin layer, (B) an intermediate layer comprising at least onepolyglycolic acid layer and embedded in the thermoplastic polyesterresin layer, (C) an end of an opening formed of a thermoplastic resinlayer alone, and (D) the rest comprising a three- or multi-layerconstruction,

(III) if necessary, the end of the opening in the multilayer preform isheat treated to crystallize the thermoplastic polyester resin layer, and

(IV) after regulated to a temperature at which stretch is possible, themultilayer preform is inserted into a blow mold cavity where themultiform preform is blow molded while a pressurized fluid is blownthereinto.

BRIEF EXPLANATION OF THE DRAWINGS

FIGS. 1, 2, 3 and 4 are illustrative in section of typical examples ofco-injection molding, and

FIG. 5 is illustrative in section of one embodiment of the multilayercontainer according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

1. Polyglycolic Acid

The polyglycolic acid used herein is a homopolymer or copolymercontaining a repeating unit represented by the following formula (1):

The proportion of the repeating unit having formula (1) contained in thepolyglycolic acid is at least 60% by weight, preferably at least 70% byweight, and more preferably at least 80% by weight, with the upper limitplaced at 100% by weight. As the proportion of the repeating unit havingformula (1) is too low, gas barrier properties and heat resistance drop.

In addition to the repeating unit having formula (1), the polyglycolicacid may contain at least one of repeating units such as thoserepresented by the following formulae (2) to (6).

Where n is equal 1 to 10 and m is equal 0 to 10.

Where J is equal 1 to 10.

Where R₁ and R₂ are each independently a hydrogen atom or an alkyl grouphaving 1 to 10 carbon atoms, and k is equal to 2 to 10.

If other repeating units having formulae (2) to (6) are introduced inthe polyglycolic acid at a proportion of at least 1% by weight, then themelting point of a poly-glycolic acid homopolymer can be lowered. With adecrease in the melting point of the polyglycolic acid, it is possibleto lower its processing temperature and, hence, reduce its thermaldecomposition upon melt processing. The crystallization rate of apolyglycolid acid can be controlled by copolymerization, so that itsprocessability can be improved. As the proportion of the other repeatingunits contained in the polyglycolic acid becomes too high, crystallinityinherent in polyglycolic acid is adversely affected, producing harmfulinfluences on gas barrier properties, etc.

Polyglycolic acids may be synthesized by dehydration andpolycondensation of glycolic acid, dealcoholization and polycondensationof an alkyl ester of glycolic acid, ring-opening polymerization ofglycolide, etc. Among these, preference is given to the synthesis ofpolyglycolic acids by a ring-opening polymerization process whereinglycolide is heated to a temperature of about 120° C. to about 250° C.in the presence of a small amount of a catalyst (e.g., cationiccatalysts such as tin organic carboxylates, tin halogenides and antimonyhalogenides) for ring-opening. The ring-opening polymerization shouldpreferably rely on bulk polymerization or solution polymerization.

According to each of the above synthesis processes, copolymers ofpolyglycolic acid may be synthesized by copolymerization of glycolide,glycolic acid or an alkyl ester of glycolic acid in suitablecombinations with a comonomer or comonomers such as cyclic monomers, forinstance, ethylene oxalate, lactide, lactones (e.g., β-propiolactone,β-butyrolactone, pivalolactone, γ-butyrolactone, δ-valerolactone,β-methyl-δ-valerolactone, ε-caprolactone), trimethylene carbonate and1,3-dioxane; hydroxycarboxylic acids, for instance, lactic acid,3-hydroxypropanoic acid, 3-hydroxybutanoic acid, 4-hydroxybutanoic acidand 6-hydroxycaproic acid, or an alkyl ester thereof; a substantiallyequimolar mixture of an aliphatic diol such as ethylene glycol or1,4-butanediol and an aliphatic dicarboxylic acid such as succinic acidand adipic acid or an alkyl ester thereof.

The polyglycolic acid used herein should have an oxygen permeabilitycoefficient of up to 5.0×10⁻¹⁴ cm³·cm/cm²·sec·cmHg as measured at atemperature of 23° C. and a relative humidity (RH) of 80% persuant toJIS K-7126. With a polyglycolic acid having too large an oxygenpermeability coefficient, it is impossible to obtain any multilayercontainer excellent in oxygen gas barrier properties. In most cases, thepolyglycolic acid used herein should have an oxygen permeabilitycoefficient in the range of 1.0×10⁻¹⁴ to 5.0×10⁻¹⁴ cm³·cm/cm²·sec·cmHg.

The polyglycolic acid used herein should also have a melt viscosity ofpreferably 100 to 1,500 Pa·s, and more preferably 150 to 800 Pa·s, asmeasured at a temperature of 240° C. and a shear rate of 100 sec⁻¹.

Upon molten at a temperature exceeding 255° C., polyglycolic acid islikely to decompose, resulting in a molecular weight drop and foaming.For this reason, it is preferable to set the melt processing temperatureof poly-glycolic acid at about 240° C. When the melt viscosity ofpolyglycolic acid is too low or too high at 240° C., it is difficult todetermine any proper molding conditions for co-injection of thepolyglycolic acid and thermoplastic polyester resin.

The polyglycolic acid used herein should have a melting point (Tm) ofpreferably 200° C. or higher, and more preferably 210° C. or higher. Apolyglycolic acid has a melting point of about 220° C., a glasstransition temperature of about 38° C. and a crystallization temperatureof about 91° C. However, it is understood that those thermal propertiesof polyglycolic acid fluctuate in dependence on its molecular weight,copolymerizable component, etc.

In the invention, the neat resin of the polyglycolic acid may be used byitself; however, it is noted that a resin composition comprisinginorganic fillers, other thermoplastic resins, plasticizers, etc. addedto the polyglycolic acid may be used in a range that is not detrimentalto the object of the invention. In addition and if necessary, variousadditives such as heat stabilizers, light stabilizers, moistureproofingagents, waterproofing agents, water repellent agents, lubricants,releasing agents, coupling agents, pigments and dyes may be added to thepolyglycolic acid.

2. Thermoplastic Polyester Resin

For the thermoplastic polyester resin used herein, thermoplasticpolyester resins other than the polyglycolic acid may be used. Amongothers, preference is given to thermoplastic aromatic polyester resinsthat are composed mainly of aromatic dicarboxylic acids or their alkylesters and glycols.

Preferred thermoplastic aromatic polyester resins, for instance, includepolyethylene terephthalate (PET), and polyethylene naphthalate (PEN),and mixtures thereof.

PET is a thermoplastic polyester resin having a melting point of about255° C., a glass transition temperature of about 76° C. and acrystallization temperature of about 170° C.

PEN is a thermoplastic polyester resin having a melting point of about256° C., a glass transition temperature of about 120° C. and acrystallization temperature of about 220° C.

Besides, use may be made of copolyesters in which a part of the acidcomponent in PET is replaced by isophthalic acid or naphthalenedicarboxylate, copolyesters in which a part of the glycol component inPET is replaced by a special diol such as diethylene glycol, etc.

For the thermoplastic polyester resin, it is acceptable to use aliphaticpolyesters other than the polyglycolic acid, for instance, polylacticacid (with a melting point of about 178° C., a glass transitiontemperature of about 53° C. and a crystallization temperature of about103° C.), etc. In applications where durability is needed, however, itis preferable to use the thermoplastic aromatic polyester resins.

The thermoplastic polyester resin should have an inherent viscosity (IVvalue) of usually 0.5 to 1.5 dl/g, preferably 0.6 to 1.0 dl/g, and morepreferably 0.7 to 0.85 dl/g. The IV value (dl/g) of the thermoplasticpolyester resin may be found by measuring that of a solution of 0.5% byweight of resin in o-chlorophenol or a phenol/chloroethane (60/40% byweight) mixed solvent at 30° C. using Canon Ubbelohde Type 1B Viscometerpursuant to ASTM D4603-96.

The thermoplastic polyester resin should also have a melt viscosity (1)of preferably 100 to 300 Pa·s, and more preferably 120 to 250 Pa·s, asmeasured at a temperature of 280° C. and a shear rate of 100 sec⁻¹.

If required, the thermoplastic polyester resin may contain variousadditives such as inorganic fillers, other thermoplastic resins, heatstabilizers, light stabilizers, moistureproofing agents, waterproofingagents, water repellent agents, lubricants, releasing agents, couplingagents, pigments and dyes.

3. Clay for Nano-Composite

According to the invention, inorganic fillers may be added to thethermoplastic polyester resin, if desired. Among others, it ispreferable to add clay for nano-composites to the thermoplasticpolyester resin.

Preferable clays for nano-composites are natural smectite purified frombentonite, and primarily montmorillonite. Among others, particularpreference is given to montmorillonite that has an aspect ratio ofpreferably 200 or higher, more preferably 300 or higher, with a limitedcontent of impurities such as silica.

A thermoplastic polyester resin composition, in which 0.5 to 5% byweight of clay for nano-composites is dispersed in the thermoplasticpolyester resin, is a clay hybrid material that can have improved heatresistance with no detriment to the transparency of a thermoplasticpolyester resin layer. For instance, the use of PET with the clay fornano-composites dispersed in it contributes to a 20 to 30° C.improvement in heat deformation temperature.

The clay for nano-composites may be processed into a hybrid material bydispersion in the thermoplastic polyester resin by known intercalation,melt mixing with the thermoplastic polyester resin, or the like.

4. Desiccant

By use of the desiccant, it is possible to prevent hydrolysis ofpolyglycolic acid due to entrance of moisture from within and withoutthe multilayer container.

By way of example but not by way of limitation, the desiccants usedherein include inorganic compounds such as sodium secondary phosphate,calcium chloride, sodium chloride, ammonium chloride, potassiumcarbonate, sodium nitrate, magnesium chloride and magnesium sulfate, andorganic compounds such as cane sugar. In place of the desiccant, it isacceptable to use high water absorption resins such as a crosslinkedpolyacrylic acid (salt) and a crosslinked starch/acrylic acid salt graftcopolymer.

5. Multilayer Container

The multilayer container of the invention comprises a polyglycolic acidlayer excellent in oxygen gas barrier properties and a thermoplasticpolyester resin layer. At the body and bottom of the multilayercontainer of the invention, an inner and an outer thermoplasticpolyester resin layer are provided, and at the body and bottom of themultilayer container, an intermediate layer comprising at least onepolyglycolic acid layer is embedded in the thermoplastic polyester resinlayer. The end of an opening in the multilayer container is formed of athermoplastic polyester resin layer alone, and the body of themultilayer container is biaxially oriented. Further, the multilayercontainer is of heat resistance enough to stand up to a 20-secondhot-filling at 93° C.

FIG. 5 is illustrative in section of one embodiment of the multilayercontainer of the invention. A multilayer container 51 is constructed ofan opening end 52, a body and a bottom. At the body and bottom of themultilayer container, an outer layer 53 and an inner layer 55 are eachformed of a thermoplastic polyester resin layer, and an intermediatelayer 54 is formed of a poly-glycolic acid layer.

The opening end 52 (mouth) of the multilayer container is formed of asingle thermoplastic polyester resin layer. Therefore, the polyglycolicacid layer 54 is entirely embedded in the thermoplastic polyester resin.Generally, polyglycolic acids are good at oxygen gas barrier propertiesand carbonic acid gas barrier properties. In the invention, it is notedthat a poly-glycolic acid having particularly improved oxygen gasbarrier properties is used. However, polyglycolic acids arebiodegradable polymers sensitive to hydrolysis. For this reason, amultilayer container comprising only a combination of a polyglycolicacid layer with other resin layer is likely to undergo degradation fromthe opening end. If the polyglycolic acid layer is embedded in thethermoplastic polyester resin layer, then effective prevention ofdegradation by hydrolysis, etc. of the poly-glycolic acid layer isachievable.

The height of the multilayer container from its bottom to the tip of thepolyglycolic acid layer is here called the “implanting height”. This“implanting height” should preferably be kept constant at a height nearto the opening end and during molding. Fluctuations in the implantingheight at the time of molding gives rise to a lowering of gas barrierproperties, because the resultant multilayer container does not includea polyglycolic acid layer portion just only at the opening end but alsoat the shoulder.

While the polyglycolic acid layer of FIG. 5 is a single layer, it isunderstood that the polyglycolic acid layer may comprise two or morelayer units. By way of example but not exclusively, some multilayerconstructions are set out below. Notice that “PGA” stands for apoly-glycolic acid layer, and “Polyester” a thermoplastic polyesterresin.

Polyester/PGA/Polyester,

Polyester/PGA/Polyester/PGA/Polyester, and

Polyester/PGA/Polyester/PGA/Polyester/PGA/Polyester.

The respective thermoplastic polyester resin layers may be formed of thesame type of thermoplastic polyester resin or different types ofthermoplastic polyester resins. For instance, the thermoplasticpolyester resin 55 that gives the inner layer may be formed of a neatresin, whereas the thermoplastic polyester resin 53 that gives the outerlayer may be formed of a thermoplastic polyester resin (resincomposition) with additives such as UV absorbers and coloring agentsadded thereto. Besides, a regrind layer comprising molding scraps may beadditionally provided as an intermediate layer. If desired, thethermoplastic polyester resin may contain a clay for nano-composites.

Often, the polyglycolic acid layer comprises one or two layer units. Byuse of two or more polyglycolic acid layer units, the gas barrierproperties of the multilayer container can be enhanced, even when theirtotal thickness is substantially equal to that of the single layer.

The thickness of the total layers that form the body (side wall) of themultilayer container may properly be determined depending on what it isused for; however, that total thickness is of the order of usually 100μm to 5 mm, preferably 150 μm to 3 mm, and more preferably 300 μm to 2mm.

In applications where heat resistance or heat resistance and pressureresistance are needed, multilayer containers must have a thicker body.For instance, a heat-resistant bottle or heat-resistant,pressure-resistant bottle of 1.5 L has a weight of the order of 50 to 60g. On the other hand, an aseptic packing bottle may have a thin bodybecause of being filled up at normal temperature and pressure; a 1.5 Lbottle may have a weight of the order of 40 to 50 g.

The total thickness of the thermoplastic polyester resin layers is ofthe order of usually 50 μm to 4.5 mm, preferably 100 μm to 2.5 mm, andmore preferably 200 μm to 1 mm. The total thickness of the intermediatepolyglycolic acid layers is usually 5 μm or greater, preferably 5 to 200μm, and more preferably 10 to 100 μm. Although the polyglycolic acidlayer may be used in a single layer form, it may be provided in a splitbarrier layer wherein the polyglycolic acid layer is split into two ormore units. When the polyglycolic acid layer is provided in a singlelayer form, it is preferable to locate that layer somewhat outside ofthe central portion of multilayer construction, because what is filledis often a fluid.

The opening end 52 of the multilayer container should preferably beconfigured in such a way as to be capped by a lid. Upon heat treatmentof this opening end 52, the thermoplastic polyester resin may becrystallized. The crystallization of the opening end should preferablybe done at a preform-making stage prior to stretch blow molding. Abottomed, multilayer preform is formed by co-injection, and the openingend of that multilayer preform is then heated to about 200° C. bynear-infrared irradiation for crystallization.

In most cases, such crystallization yields spherulites that make theopening end white and opaque. The thermoplastic polyester resin thatforms the opening end has a crystallinity of usually 25% by volume orgreater, and preferably 30% by volume or greater. Especially when PET isused as the thermoplastic polyester resin, it is preferable tocrystallize the opening end by heat treatment in favor of the gasbarrier properties and heat resistance of the multilayer container.

The body of the multilayer container should preferably be thermallyfixed by heat treatment in a biaxially oriented state. Especially whenPET is used as the thermoplastic polyester resin, it is desired that thebiaxially oriented state of the body be thermally fixed by heattreatment upon stretch blow molding. Such thermal fixation ensures thatheat resistance enough to stand up to hot-filling at 80° C. or higher isgiven to the body.

However, it is understood that a multilayer container that is obtainedusing as the thermoplastic polyester resin a resin having excellent heatresistance such as PEN to make up a layer construction such asPEN/PGA/PEN or PEN/PGA/PEN/PGA/PEN can provide a heat-resistant bottlethat can be hot-filled and have improved UV barrier properties and gasbarrier properties, even without recourse to crystallization of theopening end of a multilayer preform by heat treatment or thermalfixation of the body or the whole of the container by heat treatment.

The body of the multilayer container according to the invention shouldpreferably have transparency as represented by a haze value of 4.0% orlower.

6. Production Process of Multilayer Container

According to the invention, a multilayer container is produced byco-injecting at least a polyglycolic acid and a thermoplastic polyesterresin to form a bottomed, multilayer preform and then subjecting themultilayer preform to biaxial stretch blow molding. For thepoly-glycolic acid, a gas barrier resin is used, which contains therepeating unit having the aforesaid formula (1) at a proportion of atleast 60% by weight and has an oxygen permeability coefficient of up to5.0×10⁻¹⁴ cm³·cm/cm²·sec·cmHg as measured at a temperature of 23° C. anda relative humidity of 80% pursuant to JIS K-7126.

At the step of producing the multilayer preform, a molding machineequipped with a plurality of injection cylinders is used to co-injectthe respective resin melts through one gate into a single preform moldcavity by successive or concurrent molding in one clamp operation. Atthis step, a bottomed, multilayer preform is prepared, which comprises(A) an inner layer and an outer layer, each composed of a thermoplasticpolyester resin layer, (B) an intermediate layer comprising at least onepolyglycolic acid layer and embedded in the thermoplastic polyesterresin layer, (C) the end of an opening formed of a thermoplastic resinlayer alone, and (D) the rest comprising a three- or multi-layerconstruction.

When it comes to the successive molding process, the respective resinmelts are injected through the associated cylinders at differentinjection timings in a continuous, alternate manner, so that thepreviously injected thermoplastic polyester resin forms an inner and anouter layer, and the subsequently injected poly glycolic acid forms anintermediate layer, thereby preparing a multilayer preform.

Referring to the concurrent molding process, the respective resin meltsare injected through the associated cylinders at such varied injectiontimings that the thermoplastic polyester resin is first injected, duringwhich the polyglycolic acid is injected at some point, so that bothresins are concurrently and continuously injected to prepare amultilayer preform in which an inner and an outer layer are made up ofthe thermoplastic polyester resin and the an intermediate layer is madeup of the polyglycolic acid.

The successive molding process is now explained more specifically withreference to FIGS. 1 to 4. First, a portion of a thermoplastic polyesterresin 5 is injected through an injection cylinder 3 in a cavity 2 in amold 1. Once the injection of the thermoplastic polyester resin 5 isstopped, polyglycolic acid 6 is injected through another injectioncylinder 4 into a thermoplastic polyester resin 7 molten in the cavity2. The poly-glycolic acid forms a polyglycolic acid layer 8 in thethermoplastic polyester resin 7 in a molten state. Finally, anotherportion of the thermoplastic polyester resin 5 is again injected throughthe injection cylinder 3 to fill up the mold cavity entirely. In thisway, there is obtained a multilayer preform that is sealed at its bottomwith the thermoplastic polyester resin.

With the successive molding process wherein the thermoplastic polyesterresin, polyglycolic acid and thermoplastic polyester resin are injectedsuccessively in this order, it is possible to obtain a multilayerpreform made up of two resins/five layers, and having a layerconstruction of polyester/PGA/polyester/PGA/polyester. When the finalinjection of the thermoplastic polyester resin is intentionally stoppedat the gate, there is obtained a multilayer preform made up of tworesins/three layers, and having a layer construction ofpolyester/PGA/polyester.

With the concurrent molding process, a multilayer preform made up of twotypes of resins and three layers is generally obtainable. By applicationof the successive or concurrent molding process in various manners withmore injection cylinders, varying molding conditions, etc., it ispossible to prepare multilayer preforms having a number of multilayerconstructions.

At the step of molding mutilayer preforms by the concurrent moldingprocess, the melt viscosities of the respective resins upon co-injectionshould preferably be controlled such that the ratio (η_(T)/η_(P)) of themelt viscosity (η_(T)) of the thermoplastic polyester resin to the meltviscosity of (η_(P)) of the polyglycolic acid, as measured at themelting temperatures of the respective resins and the shear rate of 100sec⁻¹, is 1 or lower.

At the step of molding multilayer preforms by co-injection molding inthe concurrent molding process, for instance, two different resins flowthrough the mold cavity in a laminar state. Here, if the meltviscosities of both resins in a molten state are controlled, then theinner and outer layers will be formed of the thermoplastic polyesterresin and the intermediate (core) layer will be formed of thepolyglycolic acid. To this end, it is desired that control be carriedout such that the melt viscosity of the thermoplastic polyester resinbecomes lower than that of the polyglycolic acid. The melt viscosityratio (η_(T)/η_(P)) should preferably be in the range of 0.3 to lessthan 1. The preferable melt viscosity ratio can be adjusted by controlof the type and melting temperature (injection temperature) of eachresin.

When the thermoplastic polyester resin is PET, the resin temperatureupon co-injection molding is usually in the range of 265 to 290° C. Inthe case of the poly-glycolic acid, on the other hand, the resintemperature upon co-injection molding is usually in the range of 225 to260° C. Within the range of the respective resin temperatures, it isdesired that control be conducted such that the melt viscosities of therespective resins meet the above relations.

Preferably in the invention, the opening end of the multilayer preformis heat treated for crystallization of thermoplastic polyester resinlayer. Often, the opening end of a bottomed, multilayer preform has asingle thermoplastic polyester resin layer structure, and so is lessthan satisfactory in terms of heat resistance and gas barrierproperties. For this reason, it is desired that prior to subjecting thepreform to stretch blow molding, the opening end be heated to about 200°C. by irradiation with infrared rays as an example for crystallization.The post-crystallization crystallinity of the thermoplastic polyesterresin at the opening end is usually 25% by volume or greater, andpreferably 30% by volume or greater.

In the invention, use may also be made of a process wherein a resinhaving a high glass transition temperature, such as a polycarbonate orpolyallylate resin, is injection molded into a mouth piece, and themouth piece is then insert molded into the opening end of the preform,thereby improving the heat resistance of the mouth of the multilayercontainer.

The multilayer preform is then subjected to stretch blow molding. At thestretch blow molding step, the multilayer preform is regulated at atemperature at which it is stretchable, and then inserted into a blowmold cavity, where stretch blow molding is carried out with apressurized fluid such as air blown therein. Stretch blow molding may becarried out in either a hot-parison method or a cold-parison method. Itis here noted that the “parison” means a preform.

After preheating, a pressurized air such as compressed air is blown inthe bottomed, multilayer preform heated to a stretch temperature forexpansion and stretching. In general, the stretch factor is of the orderof 1.5 to 3 in the axial direction and 3 to 5 in the circumferentialdirection. Although varying slightly depending on stretch blow moldedcontainers (blow molded bottles), the blow-up ratio (total stretchfactor) is of the order of 6 to 9 for general-purpose blow moldedbottles, 8 to 9.5 for pressure-resistance bottles, 6 to 7.5 forheat-resistant bottles, and 7 to 8 for large bottles.

For crystalline resins, stretch blow molding is generally carried out inthe temperature range of the glass transition temperature to thecrystallization temperature inclusive of the resins. When thethermoplastic polyester resin is a non-crystalline resin like PETG,stretch blow molding is conducted in the temperature range of the glasstransition temperature (about 81° C. for PETG) to the meltingtemperature (about 180° C. or higher for PETG) inclusive of the resin,because there is no definite crystallization temperature or meltingpoint.

When the thermoplastic polyester resin is PET, compressed air is blownin the multilayer preform at a temperature ranging from the glasstransition temperature to the crystallization temperature inclusive ofPET, preferably at a temperature of 80 to 170° C., wherein a stretchingrod is inserted for biaxial stretching in the axial (longitudinal) andcircumferential (lateral) directions. The intermediate polyglycolic acidlayer has a glass transition temperature of about 38° C., and so iseasily stretchable following the stretching of the thermoplasticpolyester resin that forms the inner and the outer layer.

At the stretch blow molding step, it is desired that while the mold hasbeen heated to a temperature of 100° C. or higher, the biaxiallyoriented body of the multilayer container be thermally fixedsimultaneously with stretch blow molding. Heat treatment occurring inthe mold heated to such a high temperature ensures that the biaxiallyoriented state is thermally fixed and, at the same time, thecrystallization of the thermoplastic polyester resin progresses. Theheat treatment also ensures that internal distortion resulting from thestretch blow molding step is relaxed, ending up with promotedorientation and crystallization. Unlike large pherulites created by theheat treatment of the opening end, the oriented crystals in the bodywell keep transparency, even when the orientation and crystallization ofthe body are promoted. The post-thermal fixation crystallinity of thebody sidewall is usually 28% by volume or higher.

Especially when PET is used as the thermoplastic polyester resin, thethermal fixation should preferably be done in favor of heat resistance.When a multilayer container having heat resistance well fit forhot-filling is produced, the body of the multilayer container is heattreated (thermally fixed) in a stretch blow mold simultaneously withstretch blow molding, while the mold has been heated to a temperature of100° C. or higher, for the purpose of preventing thermal shrinkage anddeformation of the container at the time of hot-filling. Morespecifically, the mold is heated to a temperature of 100 to 165° C., andpreferably 145 to 155° C. for general-purpose heat-resistant containersand 160 to 165° C. for containers of high heat resistance. Althoughvarying with the thickness of multilayer containers and the heattreatment temperature applied, a heat treatment time of usually 1 to 30seconds, and preferably 2 to 20 seconds is used.

For heat treatment in the mold, several processes may be used; onecarried in a single-stage molding method wherein stretch blow moldingand thermal fixation take place in a single mold, another process in atwo-stage blow method wherein a multilayer container subjected toprimary stretch blow molding is removed from a mold and thermally fixed,and then subjected to secondary stretch blow molding in a secondarymold, yet another process in an oven blow method, etc. When the heattreatment is carried out at the time of stretch blow molding, theresultant multilayer container is removed from within the mold afterfully cooled.

EXAMPLES

The present invention is now explained more specifically with referenceto inventive examples as well as comparative examples. Various physicalproperties and other properties are measured and evaluated as follows.

(1) Melt Viscosity (η):

A sample was prepared by crystallization of an about 0.2 mm thicknon-crystalline sheet of each resin by a 5-minute heating at 150° C.Using Capillograph 1C (die=1 mmφ×10 mmL) made by Toyo Seiki Co., Ltd.,the melt viscosity of the sample was measured at a shear rate of 100sec⁻¹ and at a resin temperature of 240° C. for poly-glycolic acid and280° C. for PET.

(2) Glass Transition Temperature, Crystallization Temperature, andMelting Point:

Glass transition temperature, crystallization temperature, and meltingpoint were measured using. DSC7 made by Perkin Elmer Co., Ltd. pursuantto JIS K-7121. The heating rate and the cooling rate were alike 20°C./min.

(3) Crystallinity:

About 5 g of sample were cut out of the crystallized portion of amultilayer container, and then precisely weighed. This sample wasinserted into a densitometer AccuPyc 1330 made by Shimadzu Corporationto measure its density. This meter is designed to measure volume usinghelium gas, and as the aforesaid weight is entered therein, density isautomatically indicated. Based on density measurement, crystallinity iscalculated. The measurement temperature is 23° C.

(4) Oxygen Permeability Coefficient:

Measurement was carried out at a temperature of 23° C. and 80% RHpursuant to JIS K-7126, using Oxtran 2/20 made by Modern Controls Co.,Ltd.

(5) Oxygen Permeability of Multilayer Container:

Using a multilayer container having a volume of 1,500 ml on Oxtran-100made by Modern Controls Co., Ltd., the oxygen permeability of themultilayer container was measured at a measurement temperature of 20° C.while the inside of the container was kept at 100% RH (relativehumidity) and the outside at 65% RH.

(6) Moldability:

For instance, whether or not there were fluctuations in the implantingheight of the intermediate layer (the height of a bottle from its bottomto the tip of a poly-glycolic acid layer) was observed to makeestimations on the following ranks:

A: Superior Moldability,

B: General-Duty Moldability, and

C: Inferior Moldability.

(7) Heat Resistance:

Hot water of 80° C. was hot-filled in a multilayer container, which wasthen allowed to stand alone for 1 minute. How the opening end and thebody of the multilayer container were deformed or shrunk was observed tomake estimations on the following ranks:

-   A: Neither deformation nor shrinkage was observed, and-   B: Deformation or shrinkage was observed.    (8) Transparency:

The body of a multilayer container was cut out, and its haze value wasmeasured to make estimations on the following ranks:

-   A: A haze value of 4.0% or less,-   B: A haze value exceeding 4.0 but not exceeding 5.0%, and-   C: A haze value exceeding 5.0%.

Example 1

A homopolymer (with a glass transition temperature of 38° C., a meltingpoint of 221° C. and a crystallization temperature of 91° C.) having amelt viscosity [η_(P)] of 500 Pa·s, as measured at a temperature of 240°C. and a shear rate of 100 sec⁻¹, was used for polyglycolic acid. Thispolyglycolic acid had an oxygen permeability coefficient (PO₂) of2.5×10⁻¹⁴ cm³·cm/cm²·sec·cmHg, and a carbonic acid permeabilitycoefficient (PCO₂) of 8.9×10⁻¹⁴·cm³·cm/cm²·sec·cmHg, the latter beingmeasured using a double-side moistening gas permeability tester made byGL Sciences Inc.

A PET (with an IV value of 0.8 dl/g, a glass transition temperature of75° C., a melting point of 252° C. and a crystallization temperature of150° C.) having a melt viscosity [η_(T)] of 190 Pa·s, as measured at atemperature of 280° C. and a shear rate of 100 sec⁻¹, was used for athermoplastic polyester resin.

After pre-dried for full removal of moisture, these resins wereco-injection molded in a mold cavity by the successive molding processusing a co-injection molding machine (a renovated version of ASB-250Tmade by Nissei Co., Ltd.) for two different resins/five layers whereinthe leading portion of an injection cylinder on an inner/outer layer(PET) side was set at a temperature of 280° C., the leading portion ofan injection cylinder on an intermediate layer (polyglycolic acid) sideat a temperature of 240° C. and a merging hot runner block at atemperature of 265° C., thereby preparing a bottomed preform having amultilayer structure wherein the end of an opening had a single PETlayer structure and the intermediate polyglycolic acid layer wasembedded in the PET layer. Layer construction was a five-layer one ofPET/PGA/PET/PGA/PET.

The opening end of this multilayer preform was heated by infraredirradiation to 200° C. for crystallization. Then, stretch blow moldingwas carried out by blowing compressed air in a stretch blow mold cavityat a resin temperature of 160° C. and a stretch factor (blow-up ratio)of about 6 (about 2 in an axial direction and about 3 in acircumferential direction). While the mold had been heated to atemperature of 160° C., a multilayer container was heat treated for 5seconds at the time of stretch blow molding, thereby thermally fixingthe whole container including its body.

After that, the compressed air was changed over to cooling air which wasregulated to a temperature of 5° C. for internal cooling and then flowedthrough the mold, immediately whereupon the multilayer container wasremoved from the mold, and then slowly cooled, thereby obtaining amultilayer container product having an internal volume of 1,500 ml and aPET/PGA/PET/PGA/PET layer construction, wherein the opening end had asingle PET layer, the body and bottom were formed of the polyglycolicacid layer and the polyglycolic acid layer was embedded in the PETlayer.

The weight of the preform was about 50 g. The total layer thickness ofthe multilayer container product was 330 μm, the total thickness of theinner and outer layers and the intermediate PET layer was 300 μm, andthe thickness of the polyglycolic acid layers was 15 μm for each layerand 30 μm in all. The crystallinity of the opening end of the multilayercontainer product was 31% by volume or greater.

Example 2

Example 1 was repeated with the exception that the injection of PET wasintentionally stopped at a gate portion at the time of preparing apreform by co-injection. In this way, there was obtained a multilayercontainer product which had a layer construction of PET (100 μm)/PGA (30μm)/PET (200 μm) as viewed from the outer layer and in which the openingend was made up of a single PET layer, the body and the bottom were eachmade up of a polyglycolic acid layer and a polyglycolic acid layer wasembedded in the inner and the outer PET layer. The weight of the preformwas about 50 g, the total layer thickness of the multilayer containerproduct was 330 μm, the total PET layer thickness of the inner and outerlayers was 300 μm, and the thickness of the polyglycolic acid was 30 μm.

Comparative Example 1

A multilayer container product was molded as in Example 2 with theexception that MXD6 nylon (P-6001 made by Mitsubishi Gas ChemistriesCo., Ltd. with a melting point of 243° C., a glass transitiontemperature of 75° C., a crystallization temperature of 163° C. and anMI of 7 g/10 minute) was used in place of the polyglycolic acid.However, the leading end of an injection cylinder on the inner/outerlayer (PET) side was set at a temperature of 280° C., the leading end ofan injection cylinder on the intermediate layer (MXD6 nylon) side at260° C., and a merging hot runner block at 270° C. The weight of thepreform was about 50 g, the total layer thickness of the body of themultilayer container product was 330 μm, the total thickness of theinner and outer PET layers was 300 μm, and the thickness of the MXD6nylon layer was 30 μm.

Comparative Example 2

A multilayer container product was molded as in Example 2 with theexception that EVOH resin (DC3212 made by Nippon Synthesis ChemistriesCo., Ltd. with a melting point of 183° C., a glass transitiontemperature of 61° C., a crystallization temperature of 160° C. and anMI of 12 g/10 minute) was used in place of the polyglycolic acid.However, the leading end of an injection cylinder on the inner/outerlayer (PET) side was set at 270° C., the leading end of an injectioncylinder on the intermediate layer (EVOH) side at 200° C., and a hotrunner block where PET and EVOH merged together at 260° C. The weight ofthe preform was about 50 g, the total thickness of the body of thecontainer was 330 μm, the total thickness of the inner/outer PET layerswas 300 μm, and the thickness of the EVOH layer was about 30 μm.

Comparative Example 3

A multilayer container product was molded as in Example 2 with theexception that neither was crystallization of the opening end of thepreform conducted, nor was any heat treatment carried out in the moldupon stretch blow molding. The weight of the preform was about 50 g, thetotal layer thickness of the body of the multilayer container productwas 330 μm, the total thickness of the inner/outer PET layers was 300μm, and the thickness of the polyglycolic acid was 30 μm.

Example 3

In Example 1, a polyethylene terephthalate (PEN) homopolymer (with amelting point of 265° C., a glass transition temperature of 120° C. anda crystallization temperature of 220° C.) was used in place of the PET,and neither was the crystallization of the opening end of the preformconducted, nor was the thermal fixation of the container body carriedout in the mold. Otherwise, Example 1 was repeated to prepare amultilayer container product. This multilayer container product had heatresistance enough to stand up to not only hot-filling but also boiling,and improved oxygen gas barrier properties as well.

Example 4

A multilayer container product was prepared as in Example 1 with theexception that a PET/clay nano-composite (PET containing 3% by weight ofclay for nano-composites) obtained according to the method set forth inANTEC 2000 pp-2412 was used in place of PET. The resultant multilayercontainer product was somewhat higher in oxygen permeability than thatof Example 1, and had heat resistance enough to stand up to not onlyhot-filling but also boiling as well as improved oxygen gas barrierproperties.

TABLE 1 Examples Comparative Examples 1 2 3 1 2 3 Body sidewall ofcontainer Layer construction PET/PGA/PET/ PET/PGA/PET PEN/PGA/PENPET/MXD6/PET PET/EVOH/PET PET/PGA/PET PGA/PET Thickness (μm) 330 330 330330 330 330 PET layer (total) 300 300 300 300 300 300 (3 layers) (2layers) (2 layers) (2 layers) (2 layers) (2 layers) Other layer (total)30 30 30 30 30 30 (2 layers) (1 layer)  (1 layer)  (1 layer)  (1 layer) (1 layer)  Stretch factor Blow-up ratio about 6 about 6 about 6 about 6about 6 about 6 Axial direction about 2 about 2 about 2 about 2 about 2about 2 Circumferential about 3 about 3 about 3 about 3 about 3 about 3direction Opening end Heat treatment applied applied not applied appliedapplied not applied Crystallinity (vol. %) ≧30 ≧30 — ≧30 ≧30 — Thermalfixation applied applied not applied applied applied not applied (145°C./10 sec) Oxygen permeability 0.005 0.007 0.004 0.03 0.01 0.005(cc/bottle'day) Moldability A A A B C A Heat resistance at 93° C. A A AA A B for 20 seconds Transparency A B A C C A

With the multilayer container product (Comp. Ex. 2) wherein theintermediate layer was used in combination with the EVOH layer, moldingwas difficult to achieve, because of poor flowability and stretchabilityof resins under molding conditions, defective appearances due tovariations in the thickness distribution of the EVOH layer andfluctuating implanting height, and unsatisfactory heat stability.

The multilayer container product of Example 1 has improved oxygenpermeability, because the intermediate layer is divided into two layerunits to achieve a split barrier system.

The above examples were carried out in the hot-parison method; however,even when the cold-parison method was applied to both the layerconstructions of Examples 1 and 2, it was found that satisfactoryresults were alike obtainable.

The multilayer container or stretch blow molded product of Example 3 hadheat resistance enough to stand up to boiling treatments even withoutrecourse to the crystallization of the opening end and the heattreatment of the container body in the mold, because PEN was used forthe thermoplastic polyester resin.

INDUSTRIAL APPLICABILITY

The present invention provides a multilayer container significantlyimproved in terms of gas barrier properties, heat resistance,moldability, transparency and durability, and its production process.Having by far higher oxygen, and carbonic acid gas barrier properties,the multilayer container of the invention may be used in the form ofvarious bottles, wide-mouthed bottles, cups or the like. The multilayercontainer of the invention has also heat resistance enough to stand upto hot-filling.

1. A multilayer container production process comprising the steps ofco-injecting at least polyglycolic acid and a thermoplastic polyesterresin to form a bottomed multilayer preform, and then subjecting saidmultilayer preform to biaxial stretch blow molding, thereby producing amultilayer container having a heat resistance sufficient to withstandhot-filling at 93° C. for 20 seconds, wherein a body of the multilayercontainer is formed of layers having a total thickness of 150 μm-3 mmand has a haze value not exceeding 50% and wherein: (I) saidpolyglycolic acid is a gas baffler resin that contains a repeating unitrepresented by formula (1) at a proportion of at least 60% by weight,has a melt viscosity (η_(P)) of 150 to 800 Pa·s as measured at atemperature of 240° C. and a shear rate of 100 sec⁻¹ and ishydrolysable, and has an oxygen permeability coefficient of up to5.0×10⁻¹⁴ cm³·cm/cm²·sec·cm Hg as measured at a temperature of 23° C.and a relative humidity of 80%,

Formula (1) and said thermoplastic polyester resin is at least onethermoplastic aromatic polyester resin selected from the groupconsisting of polyethylene terephthalate (PET) and polyethylenenaphthalate (PEN), and has an inherent viscosity of 0.6 to 1.0 dl/g anda melt viscosity (η_(T)) of 100 to 300 Pa·s as measured at a temperatureof 280° C. and a shear rate of 100 sec⁻¹, (II) in the co-injecting step,a molding machine equipped with a plurality of injection cylinders isused to co-inject resin melts through one gate into a single preformmold cavity by successive or concurrent molding in one clampingoperation, wherein the polyglycolic acid resin temperature uponco-injection molding is in the range of 225 to 260° C., wherein (a) whenthe multilayer preform is prepared by successive molding, respectivemolten resins are injected through associated cylinders at such variedtimings that said molten resins are continuously and alternatelyinjected so that a previously injected thermoplastic polyester resin isformed into the inner and outer layers and a subsequently injectedpolyglycolic acid is formed into the intermediate layer, and (b) whenthe multilayer preform is prepared by concurrent molding, respectivemolten resins are injected through the associated cylinders at suchvaried timings that the thermoplastic polyester resin is first injected,during which the polyglycolic acid is injected at some point so thatboth resins are concurrently and continuously injected to form thethermoplastic polyester resin into the inner and outer layers and thepolyglycolic acid into the intermediate layer, thereby making abottomed, multilayer preform comprising (A) an inner layer and an outerlayer, each composed of a thermoplastic polyester resin layer, (B) anintermediate layer comprising at least one polyglycolic acid layer andembedded in the thermoplastic polyester resin layers withoutinterleaving an adhesive layer between the polyglycolic acid layer andthe thermoplastic polyester resin layers, (C) an end of an openingformed of a thermoplastic polyester resin layer alone, and (D) the restcomprising a three- or multi-layer construction at least including aninner layer and an outer layer each composed of a thermoplasticpolyester resin layer and an intermediate layer comprising at least onepolyglycolic acid layer embedded in the thermoplastic polyester resinlayers, whereby the outer layers of thermoplastic polyester resin inwhich the intermediate polyglycolic acid layer is embedded protect thepolyglycolic acid from hydrolysis, (III) when the thermoplasticpolyester resin is a polyethylene terephthalate (PET), the end of theopening in the multilayer preform is heat treated to crystallize thethermoplastic polyester resin layer, and (IV) after being regulated to atemperature at which stretch is possible, the multilayer preform isinserted into a blow mold cavity where the multilayer preform is blowmolded while a pressurized fluid is blown thereinto, and, when thethermoplastic polyester resin is a polyethylene terephthalate (PET),while the mold has been heated to a temperature of 100 to 165° C., abiaxially oriented body of the multilayer container is thermally fixedsimultaneously with stretch blow molding.
 2. The production processaccording to claim 1, wherein at the step (II), the multilayer preformis prepared by concurrent molding, wherein the melt viscosity of eachresin upon co-injection is controlled in such a manner to provide aratio (η_(T)/η_(P)) of 0.3 to less than 1, where η_(P) is the meltviscosity of the polyglycolic acid and η_(T) is the melt viscosity ofthe thermoplastic polyester resin, each measured at a meltingtemperature thereof and a shear rate of 100 sec⁻¹.
 3. The productionprocess according to claim 1, wherein the thermoplastic polyester resinis polyethylene terephthalate (PET) and wherein at the step (III), theopening end of the multi-layer preform is heat treated to crystallizethe thermoplastic polyester resin layer to a crystallinity of 25 vol %or higher.
 4. The production process according to claim 1, wherein atthe step (IV), biaxial stretch blow molding is carried out at a stretchfactor of 1.5 to 3 in an axial direction and 3 to 5 in a circumferentialdirection.
 5. The production process according to claim 1, wherein theintermediate layer of polyglycolic acid has a thickness of 5-200 μm. 6.The production process according to claim 1, wherein the intermediatelayer of polyglycolic acid has a thickness of 10-100 μm.
 7. Theproduction process according to claim 1, wherein the multilayercontainer is formed of layers having a total thickness of 300 μm-2 mm.